1. Field of the Invention
The present invention relates to an integrated circuit (IC) and more particularly, to a complementary metal oxide semiconductor (CMOS) IC which includes an on-board microprocessor, an analog-to-digital (A/D) subsystem, and various input/output devices on a single monolithic chip for use in various types of electrical equipment, such as circuit breakers, motor controllers, contractors and the like for converting analog signals, such as electrical voltages and currents to digital signals for monitoring and control.
2. Description of the Prior Art
There has been a recent trend over the years to utilize digital logic circuitry to control and monitor various types of electrical equipment, such as circuit breakers, motor controllers, and the like, in various industrial, commercial and utility applications. Such circuitry generally consists of four parts or function blocks. One function block generally consists of power supply circuitry to provide a relatively stable voltage to the IC. Another function block generally consists of a microprocessor for allowing the control function to be programmed by a unique set of user generated instructions, for example, software. Since many of the conditions to be monitored are analog (e.g., electrical voltages and currents) an (A/D) converter is necessary to convert these analog values to digital values. The magnitudes of such electrical voltages and currents can be on the order of 120 volts and 5 amperes, respectively. Because such magnitudes would be destructive to most IC's, signal conditioning circuitry is provided to produce usable values for the IC.
Whether the four function blocks are included on a single IC or multiple IC's depends on the state of the art of the IC processing technologies available. Because of the ability to match transistors within an IC, for example, for forming operational amplifiers, bipolar technology, is generally favored for analog or linear circuits. CMOS is generally used for digital applications. However, the current inability to match transistors relatively closely utilizing a CMOS process has heretofore made it rather impractical for use in analog circuits because of the relatively large differential offsets created in operational amplifiers by this inability. Accordingly, given the superior performance characteristics of the bipolar process for analog circuits, the hybrid control analog digital circuitry for the four function blocks identified above is generally accomplished with two or more IC's. However, the use of two or more IC's greatly increases the cost of the circuitry and also the space requirements because of the number of components and the interconnections required therebetween. In many applications, such as in circuit breakers and motor controllers, space requirements are at a premium. Thus, the use of a plurality of IC's dictates that either the circuitry be located external to the device or the size of the device has to be increased. Both options are relatively expensive.
In order to take advantage of the performance characteristics of a bipolar process for analog or linear circuitry and CMOS for digital circuitry on a monolithic chip, a hybrid bipolar-CMOS (biCMOS) process for manufacturing a single IC has evolved. However, due to the complexity of the biCMOS process, it is relatively expensive.
Another problem with designing hybrid circuitry for use in control and monitoring electrical equipment is that such circuitry is often application specific. Thus, such IC's cannot be readily adapted for use in applications other than those for which they are designed. For example, an IC having predetermined functions that are designed for use in a circuit breaker, may be inappropriate for use in a motor controller or the like. Thus, for various end users with different types of electrical equipment, separate custom IC's have to be utilized for each different type of equipment. This can be relatively expensive.